If a 17 year old football player wants to rape a 15 year old girl, he’s not going to let his drunk buddy jumping on the bed stop him. Also, other than Ford, BK has not—credibly or not credibly—otherwise been accused of forcible attempted rape. I think it is unlikely that a 17 year old male who attempted forcible rape on a stranger at a party would not have tried it again.
I think there are 4 primary options:
1. She’s lying
2. Some version of it happened but it is a case of mistaken identity
3. Some version of it happened with BK but she is misremembering and exaggerating the threat posed by BK
4. He’s lying
Because of the above, assuming she is believable, I think 3 is more likely than 4.